June 05, 2006

Self-assembly advance: copying sponges

Now researchers at the University of California, Santa Barbara (UCSB), using clues gleaned from marine sponges, have developed a method of synthesizing semiconducting materials with useful structures and novel electronic properties. The first applications could be ways to make materials for more powerful batteries and highly efficient solar cells at a lower price.

They are accessing structures that in some cases had never been achieved before. And in some cases have discovered electronic properties that had never been known before for that class of materials. Daniel Morse, professor of molecular genetics and biochemistry at UCSB, led the project. The method works with a wide variety of materials. So far, he says, the group has made 30 different kinds of oxides, hydroxides, and phosphates.

The scientists developed a synthesis method that uses the basic principles behind the natural assembly method: slow catalysis and the use of a physical template. They found they were able to assemble not only glass, but also a variety of semiconducting materials that could be useful in devices.

The method begins with a solution of molecular precursors. The researchers then expose the solution to ammonia vapor, which, as it slowly diffuses into the solution, acts as a catalyst. The physical template for the material is the surface of the solution. At this surface, where the vapor concentration is greatest, the material forms a thin film.

The method works at low temperatures, about room temperature, whereas conventional techniques for making semiconducting thin films require a high temperatures -- 400 degrees Celsius. It also does not require oft-used harsh acids and bases. In addition to making the process cheaper and easier, the mild conditions could lead to devices that incorporate materials (like dopants that would be destroyed with higher temperatures) that would be impossible to use with conventional processes